A dissertation submitted in partial ful{uFB01}llment of the requirements for the degree of Doctor of Philosophy, School of Environment, Resources and Development

Thesis (Ph.D.) - Asian Institute of Technology, 2003

Most drug delivery systems currently applied are using biodegradable, biocompatible natural biopolymers and capable of rate and/or time controlled release of drug molecules. The potential therapeutic advantages of such delivery systems have been several fold: in vivo predictability of release rate on the basis of in vitro data; minimized peak plasma levels and thereby reduced risk of adverse reactions, predictable and extended duration of action, reduced inconvenience of frequent redosing and thereby hence improve patient compliance. Such potential advantages have in fact proved to be of great therapeutic significance. Emphasis is placed on the {uFB02}at plasma level pro{uFB01}le. For all categories of treatment, a major challenge is to de{uFB01}ne the optimal dose, time, rate and site of delivery. One of the major research interests is focused in the pharmaceutical sector to expand the system that can be used for the encapsulation or incorporation of drug molecules (active substances) in a biodegradable and biocompatible polymer. Among many biopolymers, chitosan seems as ef{uFB01}cient compounds to be applied for controlled drug delivery systems for the use of various drugs. Chitosan is a deacetylated form of chitin. Chitin is biocompatible, chemically inert and biodegradable. Chitin is widely found in the exoskeleton of shell{uFB01}sh, crustaceans, arthropods, arachnids, and cell wall of fungi. In this study, chitosan has been explored for application in controlled and sustained drug delivery. This study mainly focuses on the technologies to prepare beads (diameter 400- 1000 pm), microspheres (diameter 2-15 pm) and membranes to incorporate various model compounds to be used in controlled drug delivery. In developing the technologies for controlled drug delivery, chitosan was explored for oral drug delivery using various ways of preparations such as cross{u2014}linked microcapsules by gelation and microspheres by emulsi{uFB01}cation and spray drying. The primary aim of this study is to produce non-toxic, inter polymer complex or ionic cross-linked chitosan microspheres and beads. These microspheres and beads have been tested for the potential to entrap model compounds like proteins and water-soluble antibiotics and to prevent the entrapped materials to their direct exposure in harsh gastric environment thereby increasing their bioavailability. Finally, the microspheres and beads should release after gastric passage when the drugs come in contact to the intestinal system, generally at a sustainable rate. Chitosan-alginate beads loaded with the model protein bovine serum albumin (BSA) have been investigated to explore the temporary protection of protein against acidic and enzymatic degradation in the stomach. Optimum conditions were established for preparation of homogenous, spherical and smooth beads. Multilayer beads were prepared by an additional treatment of chitosan-alginate beads either with chitosan 0r alginate or both. The presence of chitosan in the coagulation bath during bead preparation resulted in increased entrapment ef{uFB01}ciency for the BSA. Release of the entrapped protein was studied during incubation in simulated gastric {uFB02}uid (SGF pH 1.2). The beads showed swelling and started to {uFB02}oat but did not show any sign of erosion. There was hardly any release of BSA. Inclusion of pepsin in the gastric {uFB02}uid did not show any {uFB01}irther effect on the properties of the beads. Release studies were done subsequently in simulated intestinal fluid (SIF pH 7.5) to mimic the physiological gastrointestinal conditions. After transfer to intestinal fluid, the beads were found to erode and to release the protein. Microscopic and macroscopic observations continued that the release of protein was brought about by the burst of the iiibeads. Chitosan reinforced calcium-alginate beads delayed the release of BSA. The multilayer beads disintegrated very slowly. There was not any effect of the enzymes, pancreatin on characteristics of BSA loaded chitosan-alginate beads. Chitosan-alginate beads released 80-90% of the model protein within 12 h while multilayer beads released only 40-50% in the same period of time. The release from chitosan-alginate beads and multilayer beads in SIF was more delayed without prior incubation in SGF. It is c0ncluded that alginate beads, reinforced with chitosan offer a wide perspective for controlled gastrointestinal passage of protein drugs. Chitosan beads were also studied for the oral controlled release of arnpicillin sodium. Ampicillin sodium is a highly water-soluble broad ~spectrum antibiotic drug with a very short half-life (1.5 h). Chitosan-alginate/ tripolyphOSphate multilayer beads were prepared by an additional treatment with either chitosan or alginate or both. The entrapment of arnpicillin was high. In this study, TPP was used for cross-linking the surface the multilayer chitosan-alginate beads to get controlled release of arnpicillin in gastric and intestinal {uFB02}uids. During incubation in simulated gastric {uFB02}uid (SGF pH 1.2), the beads showed swelling and started to float but did not show any sign of erosion. The release of the drug was affected by cross-linking of chitosan-alginate beads with tripolyphoSphate. The multilayer beads disintegrated very slowly. The release of the drug was affected by cross-linking of chitosan-alginatc beads with tripolyphosphate. The cross-linked beads were more stable even in simulated gastric {uFB02}uid with the sustained release of arnpicillin sodium. It is concluded that chitosan-alginate multilayer beads, cross-linked with TPP offer an excellent perspective for controlled gastrointestinal passage of even highly water- soluble smaller molecules. Chitosan microspheres (diameter 2-15 mm) were prepared by using solvent evaporation and spray drying method. In this study, arnpicillin sodium, a broad{u2014}spectrum antibiotic was used to demonstrate entrapment and to check the controlled release in different dissolution media. The micrOSpheres were cross-linked with tripolyphosphate. The cross-linked microspheres showed slower release and more stable than uncross-linked microspheres. The entrapped arnpicillin was found active like control against microorganism Staphylococcus aureus, evaluated by minimal inhibitory concentration (MIC) analysis. These cross-linked chitosan microspheres can be applied either in local treatment of local therapy for any infection and for systemic therapy to improve the bioavailability. In the last part of the study, various types of chitosan, processed from shrimp chitin were used to prepare thin membranes for further study. The homogenous membranes can be prepared with different pore size by the technique of phase evaporation. The membranes were characterized in the form of thickness, pore size, porosity and tensile strength. The membranes prepared from high molecular size were found having lower pore size and higher tensile strength. For this study, the test porogens for controlling the pore size used were monosodium glutamate (MSG), polyethylene glycol (PEG) and tertiary butanol (TBA). With the use of these porogens, the diameter of the pore size was reduced to 20 nm. The membranes were further loaded by salicylic acid. The release study was performed directly from single layer membranes as well as through various rate controlling (screening) membranes. The release rate of drug from single layer drug loaded membranes was faster in the first initial half-hour and shows down afterwards- In double layered membranes, the outer layer can act as a screening layer and be applied to accomplish sustained release. Chitosan membranes can be explored for the transdermal and buccal drug delivery systems. ivIn summary, chitosan as a part of the matrix either in beads, microspheres or in the membranes can greatly improve the essential features of drug delivery systems, applied in combination with alginate, calcium and tripolyphosphate. Inclusion of chitosan in this system would result in enhanced entrapment of drug and more sustained release. A funher increase of the use of chitosan in drug delivery systems is foreseen in the near future.